Why do the plates move?

The lithosphere is split into 7 large plates plus many smaller ones and these lie on the soft asthenosphere.

Two possible reasons why they move:

1.  Convection in the asthenosphere pushes the plates due to different temperatures.

2.  The plates are pulled apart by gravity and the weight of the edges as they sink.

How do we know this?

Evidence: Ridges, Trenches, Fracture Zones & The seven larger plates

Check out the map for places where the evidence occurs!